1. Field of the Invention
This invention relates to weighing scales and, more particularly, to household weighing scales utilizing a multi-string weighing system stressed in tension and vibrated at its resonant frequency for determining the magnitude of a weight applied to the scale.
2. Description of the Prior Art
It has been suggested heretofore that the weight applied to a household weighing scale be measured by means of a vibrating string, or wire, system in which a string is tensioned by a weight applied to the scale. The string is then vibrated at its natural or resonant frequency, and means including appropriate logic circuitry and electronic output displays are utilized to sense the natural frequency and convert the sensed frequency into an electronic output display of the applied weight. These systems operate on the well-known principle that the natural or resonant frequency of a string is related in a known manner to the tension force applied to the string.
In the known prior art string systems, a relatively large change in applied weight is required in order to produce an appreciable change in resonant frequency. As a result, both the input mechanism, which converts an actual weight placed on the scale to the tension force applied to the string, and the output mechanism, which senses the natural frequency and converts it into a display of the applied weight, must be extremely responsive to small changes in applied weight and frequency. Moreover, care must be taken in such systems to avoid vibration of the string at harmonic frequencies, which can result in erroneous output readings.